In processes of producing semiconductor devices, such as ICs and LSIs, fine patterning has so far been performed by photoresist composition-utilized lithography. With recent increase in packing densities of chips, there has been a growing demand for formation of superfine patterns having their widths in the region of submicrons or quatermicrons. In line with such a demand, there has been a trend toward exposure light of shorter wavelengths, namely a trend to change exposure light from g-ray to i-ray and further to KrF excimer laser light. At present, development of not only the lithography using excimer lasers but also electron-beam lithography and X-ray lithography is progressing.
In particular, the electron-beam lithography is placed as pattern-formation technology of next generation or the generation after next, and high-sensitivity, high-resolution negative resists are required therefor. Increasing the sensitivity is a very important problem, notably in reducing a wafer processing time. As to negative resists for use in electron-beam lithography, however, the pursuit of increases in their sensitivities gives rise to aggravation of line edge roughness in addition to a drop in resolution and a deterioration of pattern profiles. Therefore, it is strongly desired to develop resists meeting those characteristic requirements all together. The term “line edge roughness” as used herein means that edges are seen rough when patterns are viewed from the direction right above them because irregular undulation in the direction perpendicular to the line direction is caused in the edges of the resist pattern-substrate interface by characteristics of the resist. Transfer of this roughness occurs in the etching process using the resist as a mask, and results in deterioration of electric characteristics and lowering of yields. Particularly in the superfine region of 0.25 μm or below, an improvement in the line edge roughness is a vitally important problem. As the high sensitivity is in tradeoffs with high resolution, good pattern profiles and favorable line edge roughness, it is of great importance how to achieve satisfactory levels of improvement in all of those properties.
As resists suitable for the electron-beam lithography and the X-ray lithography, chemical-amplification resists principally utilizing acid-catalyzed reaction have been employed from the viewpoint of increasing the sensitivity. With respect to negative resists, chemical-amplification compositions containing as main components alkali-soluble resins, cross-linking agents and acid generators have been effectively used.
Hitherto, performance improvements of chemical-amplification negative resists have been studied variously, and the studies as described below have been made particularly from the standpoint of acid generators. Specifically, the acid generators to which studies have been given include the organic halogen compounds disclosed in Japanese Patent Publication No. 3635/1996, the Br- and Cl-substituted aromatic compounds disclosed in Japanese Patent Laid-Open No. 52348/1990, the aromatic compounds containing Br- and Cl-substituted alkyl and alkoxy groups as disclosed in Japanese Patent Laid-Open Nos. 367864/1992 and 367865/1992, the haloalkanesulfonate compounds disclosed in Japanese Patent Laid-Open No. 87746/1991, the iodonium compounds and the sulfonium compounds disclosed in Japanese Patent Laid-Open No. 199770/1994, the phenolic hydroxyl group-containing trifluoromethane sulfonate compounds disclosed in Japanese Patent No. 2,968,055, and the specified benzene sulfonate compounds containing phenolic hydroxyl groups as disclosed in Japanese Patent Laid-Open No. 2001-142200.
However, those compounds, even when they are used in any combinations, were unsuccessful at concurrently satisfying all the resist-performance requirements in the superfine region, namely high sensitivity, high resolution, good pattern profiles and favorable line-edge roughness.